Of equal significance with this persistency of survival in the kiva, as to both structural type and function, of the earliest cave-dwelling hut-rooms through successively higher stages in the development of cliff architecture, is the trace of its growth ever outward; for in nearly or quite all of the largest cliff ruins, while as a rule the kivas occur, as stated, along the fronts of the houses--that is, farthest out toward the mouths of the caverns--some are found quite far back in the midst of the houses. But in every instance of this kind which I have examined these kivas farthest back within the cell cluster proper are not only the oldest, but in other ways plainly mark the line of the original boundary or frontage of the entire village. And in some of the largest of these ruins this frontage line has thus been extended; that is, the houses have grown outward around and past the kivas first built in front of them, and then, to accommodate increased assemblies, successively built in front of them and in greater numbers, not once or twice, but in some cases as many as three, four, and in one instance five times. All this makes it plain, I think, that the cave and cliff dweller mode of life was a phase, not an incident merely, in the development of a people, and that this same people in general occupied these same caves continuously or successively for generations--how long it is needless here to ask, but long enough to work up adaptively, and hence by very slow degrees, each one of the little natural hints they received from the circumstances and necessities of their situation in the caves and cliffs into structural and other contrivances, so ingenious and suitable and so far-fetched, apparently, so long used, too, as to give rise to permanent usages, customs, and sociologic institutions, that it has been well-nigh impossible to trace them to such original simple beginnings as have been pointed out in the case of a few of them. The art remains of both the earliest cave dwellers and of the cliff dwellers exhibit a like continuity of adaptive development; for even where uses of implements, etc., changed with changing conditions, they still show survivals of their original, diverse uses, thus revealing the antecedent condition to which they were adapted.